Automatic Transmission Oil Supply, Function - GF27.57-P-1000ANI

Transmission 725.0 in model 253 

Function requirements, general 

• Terminal 15 ON

Automatic transmission oil supply 

Internal combustion engine ON: 

With the combustion engine running, the oil pump (primary pump) delivers oil to the electrohydraulically actuated automatic transmission. The oil pump is driven through a chain drive by the drive shaft. The oil pump is installed below the transmission bell housing behind the torque converter (transmission 725.004/008/011/041/044/048/054/058) or the wet clutch (transmission 725.096).

Internal combustion engine OFF: 

The electric auxiliary oil pump (M42) is activated when the combustion engine is stopped in start/stop mode and then becomes responsible for the basic supply of control elements and actuators. This maintains the defined basic pressure.

If, with a stationary internal combustion engine, the oil supply fails, the control elements and actuators all switch to an unloaded basic status and the automatic transmission power flow stops.

Start internal combustion engine: 

When starting the internal combustion engine, the gear must be shifted from "N" to "D1" after establishing the oil supply. The resulting loss of time between the start-off request and the start-off time is minimized by the electric auxiliary oil pump so that it is not noticeable for the driver.

The electric auxiliary oil pump also supports the primary pump at low internal combustion engine speeds. The volumetric flow rate routed as required by the electric auxiliary oil pump, is requested in the internal combustion engine's low-speed range during shift operations (filling of next actuator) or to meet increased cooling requirements.